The hypothesis that cancer results from an impairment of the process of cell differentiation will be tested in tumors of the hematopoetic system. The number of different sequences (complexity) comprising the cytoplasmic polyadenylated RNA (mRNA) and the relative abundance of these sequences will be determined. The objectives are to determine if the abundancy patterns differ among normal and malignant tissues and to determine the abundance of sequences homologous to endogenous viral-like particles in leukemic and remission states. Cytoplasmic polyadenylated RNA, which actually does not include all the mRNA species in a cell, will be isolated and 3H-cDNA probes generated by reverse transcriptase. The hybridization properties of the probe will be taken as representative of the intracellular mRNA population.